It is common practice in the construction of gate valves, ball valves and the like which employ seat rings that are accommodated in seat recesses provided in the valve body and which are spring-urged toward the movable valve member. One difficulty that has been experienced with such valves, particularly when used in systems handling petroleum liquids, is that sediment from the petroleum liquids tends to accumulate behind the seat rings, thereby interfering with the seat movement and seat positioning that is necessary for proper operation of the valve. Most petroleum products are transported and processed in piping systems and such products are frequently of corrosive nature, tending to develop internal pipe scale when the piping system is composed of ferrous metal pipe. Even under circumstances where the petroleum products and other fluids are of noncorrosive nature, ferrous metal pipe, even when new, typically has sufficient internal mill scale, welding slag and weld metal beads to be detrimental to the handling of such fluids because these ferrous materials are readily deposited in valves. Under circumstances where the seat members are of movable nature, logically they must be retained in movable relation within seat recesses and a space must exist between the seat members and rear wall surfaces of the seat recesses in order to accommodate seat movement. These annular seat recess spaces tend to accumulate sediment, especially at the lower portions thereof. Typically, there is insufficient turbulance in the flowing fluid to maintain these recesses clear of sediment deposits.
Deposits of sediment in seat recesses is especially detrimental under circumstances where portions of the gate members are removed from between the seats during opening movement. For example, in gate valves of the short gate type such as disclosed in U.S. Pat No. 3,807,688, deposits of sediment can settle in the seat pockets and jam the seats, thus restricting seat movement to the extent that it becomes difficult or impossible to move the gate member fully between the seats. In this condition, sufficient forces can be developed between the gate member and seats during closing movement to cause metal galling or other seat damage, thereby resulting in the necessity for repairing the valve to again render it usable.